High magnetic permeability Ni-Fe alloys are widely used as magnetic shielding materials such as materials for casings of magnetic heads, magnetic shielding plates for cassette tape digitizers, etc. For such magnetic shielding materials, high magnetic permeability in the low frequency bands is required as an alternating current magnetic characteristic. Often inductance specific magnetic permeability .mu..sub.L of not less than 9000 at 0.3 kHz or of not less than 4500 at 1 kHz is required. Also, with respect to direct current magnetism, often high characteristics such as coercive force Hc of not more than 0.10 Oe and saturated magnetic flux density Bs of not less than 3000 G are required.
Therefore, 80% Ni Permalloy (JIS-PC(corresponding to ASTM A753)), which contains Mo, Cr, Cu, etc. and has the highest magnetic permeability among the Ni-Fe magnetic alloys, is widely used as magnetic shielding materials. However, this alloy has a disadvantage that it is expensive, because the alloy contains no less than 80% of expensive Ni as well as the more expensive Mo. Therefore, there is a demand for an inexpensive magnetic alloy which has magnetic characteristics comparable with those of JIS-PC alloy.
The principal object of the present invention is to provide a novel soft-magnetic alloy which is provided with alternating current magnetic characteristics of the same level as those of JIS-PC alloy or better and yet is inexpensive.
We studied magnetic properties of a number of Fe-Ni . magnetic alloys and found that alloys comprising 35- 40% Ni, 5-14% Cr and balance Fe have alternating current magnetic characteristics, such as magnetic permeability, of the same level as those of JIS PC alloys or JIS PB alloys (45% Ni Permalloy) or better in spite that the Ni content is far less than the latter.